1. Field of the Invention
The present invention relates to a bipyrazole derivative and a medicine comprising the bipyrazole derivative as an active component. More particularly, the present invention relates to a bipyrazole derivative capable of capturing active oxygen and in vivo free radicals, and useful as an agent for preventing or treating various diseases induced by active oxygen or in vivo free radicals and also as a reagent for obtaining biomedical images non-invasively by way of magnetic resonance typified by ESR (Electron Spin Resonance) or for detecting active oxygen and free radicals in collected organic tissues. The present invention further relates to a medicine comprising the bipyrazole derivative as an active component.
2. Description of the Background Art
Active oxygen is defined as one type of oxygen which has a short life, but is reactive and involves in various in vivo oxidation reactions. In a narrow sense of the word, the active oxygen indicates hydroxyl radical (.OH), superoxide (O.sub.2.sup.-), singlet oxygen (.sup.1 O.sub.2), and hydrogen peroxide (H.sub.2 O.sub.2), while in a broad sense the active oxygen includes peroxidase radical (LOO.) and alkoxyl radical (LO.) originating from the reaction of said active factors and biological components (such as unsaturated fatty acid), and hypochlorite (ClO.sup.-) which is produced from H.sub.2 O.sub.2 and Cl.sup.- by the reaction with myeloperoxidase or the like. The hydroxyl radical and superoxide are radicals. "Radical" is defined as an atom or molecule which possesses one or more unpaired electrons. Although hypochlorite ion and hydrogen peroxide are not radicals themselves, these are produced by a radical reaction and induce other radical reactions. Active oxygen and radicals are generally unstable. Their life is very short, for instance, from 10.sup.-5 to 10.sup.-4 seconds in the case of benzyl radical in vapor phase, and from 10.sup.-3 to 10.sup.-2 seconds in the case of more simple radicals such as methyl radical and hydroxyl radical under ordinary pressure in vapor phase.
In recent years in the field of biology, medicine, and pharmacology, attention has been given to and studies have been undertaken relating to active oxygen and free radicals which show various in vivo physiological activities. Ultraviolet radiation, radioactive rays, air pollution, oxygen, lipid hyperoxidation, metal ions, ischemia-reperfusion, and the like can be given as the causes for in vivo formation of active oxygen and free radicals. The resulting active oxygen and in vivo free radicals induce various in vivo reactions such as hyperoxidation of lipids, denaturing of proteins, decomposition of nucleic acid, and the like. Cerebral ischemia, heart disease, digestive system disease, carcinoma, aging, inflammation, and so on can be given as the associated diseases accompanied by such reactions induced by active oxygen and in vivo free radicals. Noninvasive ex vitro detection of such active oxygen and in vivo free radicals which relate to so many diseases may help investigate the causes of a number of such diseases and provide useful medical information.
As the methods of detecting active oxygen or free radicals, there are (1) an indirect method which comprises detecting or measuring changes in absorbance or luminescence which occurs as a result of the addition of a reagent to a reaction system and (2) the ESR method in which unpaired electrons of free radicals are directly detected.
Of these, the ESR method can measure samples in the form of either solution or solid, either opaque or heterogeneous samples, so this method is very advantageous in the detection of in vivo active oxygen. However, it is difficult to measure in vivo free radicals directly by the ESR method because the in vivo free radicals are generally unstable and of short-life. In addition, active oxygen which does not have unpaired electrons cannot be measured by the ESR method.
To overcome these problems in the ESR method, a spin trap method, in which the active oxygen having unpaired electrons such as hydroxyl radicals is measured, has been developed. According to this method, a spin trap agent (T) is quickly reacted with a free radical (R.) such as a hydroxy radical having a short life as shown in the formula below. The resultant spin adduct (RT.) which is stable and has a long life is detected by the ESR method. ##STR2##
Specifically, short life active oxygen can be measured by providing a compound which rapidly reacts with radicals and produces a spin adduct which is sufficiently stable for measurement by the ESR method and adding this compound to the measurement system as a spin trap agent, and measuring the stable spin adduct thus produced.
In addition, singlet oxygen which is an in vivo active oxygen and hypochlorite ion cannot be measured directly by the ESR method due to their short life and the absence of unpaired electrons. Therefore, a method analogous to the above-mentioned spin trap method is used for their measurement. The principle of this method involves the reaction of an active oxygen detection reagent (S) with an active oxygen (Q) such as singlet oxygen which does not have unpaired electrons and has a short life, whereby the former is converted into a stable free radical according to the following formula. ##STR3##
Measurement of a short life active oxygen having no unpaired electrons becomes possible by measuring a stable free radical (S'.).
Therefore, the compound which is used as a spin trap agent or active oxygen detection reagent must satisfy the following conditions: 1 to rapidly react with active oxygen and free radicals, 2 to be converted into a sufficiently stable radical, 3 to be chemically stable during handling, and 4 to have low toxicity.
There are nitrone-type and nitroso-type compounds conventionally used as typical trap agents for the studies of in vivo free radicals. As nitron-type compounds, a cyclic nitron compound such as DMPO (5,5-dimethyl-1-pyrroline-1-oxide) and a linear nitron compound such as PBN (N-tert-butyl-.alpha.-phenylnitrone) can be given. As nitroso-type, DBNBS (sodium 3,5-dibromo-4-nitrosobenzenesulfonate) has been used. As an active oxygen detection reagent, TMPD (2,2,6,6-tetramethyl-4-piperidone) has been used. These are only compounds which have conventionally been used. However, none of them satisfy the above-mentioned conditions (see, e.g. Pharmacia, 28, 1347-1352 (1992)).
There is a strong demand for the prevention and treatment of adult diseases such as cerebral ischemia, heart disease, digestive system disease, and carcinoma, and prevention treatment of inflammation, as well as prevention of aging. Active oxygen and free radicals are known to cause these diseases. Therefore, the development of a medicine which can capture these factors and effectively prevent or treat these diseases has been desired.
As mentioned above, if there is a compound which can rapidly react with the active oxygen or in vivo free radicals and produce a stable reaction product, such a compound can be utilized as an active oxygen detection reagent in the ESR method which is a non-invasive measuring method. Such a compound will be useful in the diagnosis of diseases associated with active oxygen and in vivo free radicals such as carcinoma, ischemia, inflammation, and the like by utilizing biological spectrum or biological images of the active oxygen and in vivo free radicals.
The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems and to find a pharmaceutically safe compound which rapidly reacts with active oxygen or in vivo free radicals and produces a reaction product which is stable. As a result, the inventors have found that bipyrazole derivatives which possess a bipyrazole structure and two hydroxyl groups as shown by the following formula (I) satisfy the above-mentioned conditions and function as an active oxygen detection reagent.
The inventors have discovered that these derivatives can capture active oxygen and in vivo free radicals, and is useful as a medicine for preventing or treating such diseases as cerebral ischemia, heart disease, digestive system disease, carcinoma, aging, and inflammation, and also as a diagnostic agent or detection reagent such as a spin trap agent. These findings have led to the completion of the present invention.